A vast bulk of low-energy fluid is easy to accumulate in the three-dimensional corner range of the rear stage in a high-pressure compressor. To quantitatively analyze the correlation between suction slot position and corner separation， this paper， taking a high-load compressor cascade as the research object， discusses the influence of the axial position changes in the full-span suction slot on the cascade performance by the computational fluid dynamics （CFD） simulation software to guide suction slot design. As a result， it proposes the distance （ZCS） between the starting position of the corner separation and the leading edge of the cascade as the quantitative standard. It is found that the total pressure loss decreases first and then increases as the axial position of the suction slot moves upstream around the design working conditions， and there is an optimal axial position of the suction slot on the blade suction surface in different conditions. At the angle of incidence of 0°， the optimal performance can be achieved when the axial distance between suction slot and separation point is 0.33 times as much as ZCS， and the total pressure loss coefficient can be reduced by 10.9%. With the help of the corner separation structure， this quantitative result realizes the standardized guidance of the axial position design of the suction slot.